High temperature, low friction ceramic coating for gas turbine regenerator seals

ABSTRACT

A high temperature seal coating material adapted to be used with a rotary ceramic regenerator matrix to effect a sliding seal of one gas flow region of the regenerator with respect to another, the coating including manganese oxide as one of the constituents to provide improved hardness thereby achieving an increased seal life during operation of the rotary regenerator at high temperatures.

United States Patent 1191 Rao [ HIGH TEMPERATURE, LOW FRICTION CERAMIC COATING FOR GAS TURBINE REGENERATOR SEALS [75] Inventor: V. Durga Nageswar Rao,

Woodhaven, Mich.

[73] Assignee: Ford Motor Company, Dearborn,

Mich.

22 Filed: Apr. 15, 1974 21 Appl. No.: 461,197

[52] U.S. C1. 277/96 R; 117/93.1 PF; 165/9 [51] Int. Cl. E16,] 15/16 [58] Field of Search 277/96 R, 96 A, DIG. 6, 277/235 A; 165/9; 117/931 PF [56] References Cited UNITED STATES PATENTS 3,646,993 3/1972 Rice 277/96 [111 3,907,311 1451 Sept. 23, 1975 3,647,228 3/1972 Cassidy 277/96 3,659,861 5/1972 3,743,008 7/1973 Zeek et a1 165/9 3,746,352 7/1973 Rao 277/96 3,747,944 7/1973 Roy et a1. 277/96 Primary Examiner-Robert 1. Smith Attorney, Agent, or FirmDona1d J. Harrington; Keith L. Zerschling [57] ABSTRACT 2 Claims, No Drawings HIGH TEMPERATURE, LOW FRICTION CERAMIC COATING FOR GAS TURBINE REGENERATO SEALS I" GENERAL DESCRIPTION or THE INVENTION for adequate sea] life and to provide adequate mechanical strength. St'anic oxide is used to improve the hardness of the coating in the high temperature zone of the regenerator seal. This zone, which normally is accomi v v 5 panied by a high wear rate is at the crossarm of the seal The improvements of my inventionfrel' te e erall that separates the high-temperature, low-pressure reto coating materials for use with regenerator eals'for g ion of the regenerator matrix from the high-pressure, rotary ceramic regenerator matrixes in a gas turbine low-temperature region. At that point the gas flow pasengine. Reference may be made to my co-pending apsages 0f the generator matrix pass over the seal with a plication, Ser. No. 415,897, filed Nov. 14, 1973, for a high temperature rubbing action. Although use jof description of a gas turbine engine and seal coating mastanic oxide for seal coatings at this location of the seal terial for use with a Seal that forms a part of the gas turcontruction provides the necessary seal life due to the bine engine regenerator construction. The coating mahardness of the coating, the stanic oxide may be elimiterials for the seals described in my US. Pat. No. nated and replaced with manganese oxide, which may 3,746,352 includes zinc oxide, calcium fluoride and e be identified generically as Mn,.0,,. Typical molecules stanic oxide although other examples of suitable seal are MnO Mn O and MnO. materials under various operating conditions'also are The id f manganese are introduced in a mixture described In that p V of 70% zinc oxide and 30% calcium fluoride and used In order to improve the mechanical strength and to i the preparation f plasma Spray d Thi avoid chipping of the seal material during operation of der may be prepared in a manner d ib d i my the gas turbine regenerator at high temperatures, the pending application, Ser. NO. 415,897, filed Nov. 14, h oxhte h Calcium hhorihe Supplemente d 1973. Reference may be made to that application for with stanic oxide. I have described this improvement in a description of a method for applying a plasma spray my Both of my pnor patehts powder to the seal surface. After this is done, the surm'fty h referred to for the Purpose of Shpptemeht'hg face is sintered at a temperature of about 2200F. The thIs dtsclosute' manganese oxide should not be used in excess of 15% Although seal material for gas turbine regenerators by weight or less than 5% by weight when the base tha.t Include zmc oxIde calclum fluonde .Stamc composition ingredients are 70% by weight zinc oxide oxide (8,0 have been successful, the addition of and 30% by weight calcium fluoride. The zinc oxIde has stanic oxide greatly increases the cost of the material. a low friction co efficient but it is soft The calcium My improved Sealing material does not require the use fl uori e, as mentioned previously, provides a glaze sur of ftxpenswe Stamc oxIde although t deslrabte propface. The addition of the manganese oxide increases emes of that. cqmpolmij are retamed' S.pecl.ficany the hardness and improves the thermal cycling propermanganese oxide is substituted for the stanic oxide, although care must be taken to maintain the proper permechamcal ti tr h 3 the comcentage of manganese oxide in the seal material. I have home matefla not crum e urmg lg tempera' described this characteristic in the following particular igtgsz illgzhese o ide content exceeds 157 the Salt descri tion. The cost of in im roved seal material is reduc d to about one-half if th: cost of seal materials corrosion resistance of the coating is inadequate to containing stanic oxide 4O meet the desired operating life of the seal. On the other A seal which uses the coating described in this specihand if the mahgahee chhteht is f to less fication results in increased hardness and improves the than there Is no Stghlftcaht tmptovehttfht the thermal cycling properties as we as the mechanical chanical strength. The coefficient of friction for a seal strength of the seal. Crumbling is avoided as temperafg g ig g a g 55 3x 2: ture chan t 0 gas occur m the gas turbine cycle manganese oxide in a percentage by weight between PARTICULAR DESCRIPTION OF THE INVENTION 15% and 5% is less than 0.3. This produces a wear rate lhave described in my us. Pat. No. 3,746,352 a seal of mils or less for each 100 hours of Operation of material that includes 70% zinc oxide and 30% calcium the g turbine engine with which the Seal Is Used- .fluoride. It is suggested in that disclosure that it may be I have provided in the following table a summary of used to seal the so-called crossarm seal portion of a rothe coefficients of friction and wear rates for seals havtary regenerator seal construction. The calcium fluoing various percentages of manganese oxide when used ride provides a glazing surface for the seal and the zinc with a base composition of 70% by weight zinc oxide oxide provides those wear properties that are necessary and 30% by weight calcium fluoride.

1400" F-7 PSl wEAR TEST COMPOSlTlON 200 Hr. l400F-RT 1400 F SALT COEFF. OF WEAR IN 200 WEAR RATE BASE ZnO-30 CaF TH CYCLING TEST CORROSION TEST FRlCTlON HOURS MlLS MlLS/lOO I-IRsv +37: Mn,O,, Poor Good 0.l5-0.2 2.0 1.0 +5 2 Mn,0,, Marginal Good 0.15-0.2 2.2 1.1 +10% Mn,0,, Good Good 0.2-0.22 2.0 1.0

+15% Mn,0,, Good Satisfactory 0.2-0.25 2.0 1.0 +18% Mn,0,, Good Attacked 0.25-0.35 2.5 1.25 +20% Mn,0,, Good Poor 0.2-0.4 2.5 1.2

It will he apparent by inspecting the above tubular data that mechanical strength. as evidenced by the cycling test results, is poor for any manganese oxide percentage less than 5%. On the other hand, the salt corrosion test results are indicated to be very satisfactory for any manganese oxide percentage greater than I571.

4 powder deposit which is applied to the aforesaid seal surface, the percentage of manganese oxide being between 5% and 30% by weight.

2. The combination set forth in claim 1 wherein the ratio by weight of the zinc oxide to calcium fluoride is approximately to 30, the zinc oxide and calcium fluoride forming the base ingredients to which the manganese oxide is added. 

1. A HIGH TEMPERATURE, LOW FRICTION CERAMIC COATING FOR USE WITH A SLIDING SEAL SURFACE FOR A CERAMIC REGENERATOR CORE SEAL IN AGAS TURBINE ENGINE WHEREBY THE COATING MATERIAL IS SLIDABLY SITUATED IN SEALING ENGAGEMENT WITH THE SEALING SURFACE OF THE ROTARY CERAMIC MATRIX, SAID COATING MATERIAL COMPRISING ZINC OXIDE, CALCIUM FLUORIDE AND MAGANESE OXIDE IN THE FORM OF A SINTERED POWDER DEPOSIT WHICH IS APPLIED TO THE AFORSAID SEAL SURFACE, THE PERCENTAGE OF MANGANESE OXIDE BEING BETWEEN 5% AND 30% BY WEIGHT.
 2. The combination set forth in claim 1 wherein the ratio by weight of the zinc oxide to calcium fluoride is approximately 70 to 30, the zinc oxide and calcium fluoride forming the base ingredients to which the manganese oxide is added. 